Thermal actuator

ABSTRACT

The invention relates to a thermal actuator which comprises adjacent expansible equalizing and working chambers separated by a movable wall to which is connected an actuating member for operating a valve or the like. Spring means bias the wall in one direction and an expansible fluid in the working chamber biases the wall in the other direction in response to the operation of heating means in the working chamber. A fluid passage between the equalizing and working chambers which is controlled by an electromagneticallly operated valve permits a rapid return of the separating wall to its initial position which in turn permits the rapid return of the actuating member to its initial position.

iinited States Patent [191 Arii [ THERMAL ACTUATOR [75] inventor: Heino Arff, l-Ienstedt-Ulzburg,

Germany [73] Assignee: Danfass A/S, Nordborg, Denmark [22] Filed: Sept. 18, 1972 [21] Appl. No.: 290,092

[30] Foreign Application Priority Data 3,132,472 5/1964 Schweitzer 60/25 11] 3,834,165 [451 Sept. 10, 1974 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Allen M. Ostrager [5 7] ABSTRACT The invention relates to a thermal actuator which comprises adjacent expansible equalizing and working chambers separated by a movable wall to which is connected an actuating member for operating a valve or the like. Spring means bias the wall in one direction and an expansible fluid in the working chamber biases the wall in the other direction in response to the operation of heating means in the working chamber. A fluid passage between the equalizing and working chambers which is controlled by an electromagneticallly operated valve permits a rapid return of the separating wall to its initial position which in turn permits the rapid return of the actuating member to its initial position.

8 Claims, 2 Drawing Figures PATENTEDSEP 1 01914 3.834.165

SHEET 1 UF 2 THERMAL ACTUATOR The invention relates to a thermal actuator comprising a working chamber which is filled with an expansible fluid, heatable by a preferably electrical heating device, and which has a displaceable wall which acts on an actuating element against the force of the spring, the thermal actuator also comprising a valve which influences the pressure conditions.

Numerous thermal actuators are known in which an expansible substance undergoes expansion as a result of heating, and thus displaces the actuating element. A thermal actuator of this kind is used in particular for actuating a valve. Solid, liquid and gaseous media as well as liquid vapor charges, which evaporate and condense in dependence upon the temperature and pressure in the working chamber, can be considered for use as the expansible substances.

In a known thermal actuator (U.S. Pat. No. 3,132,472), the working chamber contains a bell-like component within thich the liquid vapor charge is heated Fitted at the top of the bell is a plurality of valves which can be opened with the aid of a magnet or by a bimetal element or the like.

A condensation zone is formed in the working chamber above the bell. When one of the valves is opened, vapor flows into this zone and is condensed there. In this way, a predetermined pressure can be maintained in the working chamber, and thus the actuating element can be set in a prescribed position.

In all the known thermal actuators considerable difficulties arise in returning the actuating element rapidly to its initial position, since the return movement depends upon the cooling rate of the expansible medium. Thermal actuators are therefore unsuitable, for example, for valves that, for safety reasons, are required to incorporate a quick-acting closing device. Nor are thermal actuators suitable for other purpoposes in which a slow forward movement is to be followed by a rapid return movement, as required for example, in the case of the drives of pumps.

The object of the present invention is to provide a thermal actuator of the initially stated kind in which the actuating element can be rapidly returned to the initial position.

According to the invention this object is achieved by the provision of an equalizing chamber which is separated from the working chamber by a displaceable wall, and by fitting the valve in a passage interconnecting the two chambers.

In this arrangement that side of the displaceable wall remote from the working chamber is not affected by the atmosphere but by the pressure in the equalizing chamber. If the valve is opened, expansible fluid flows from the working chamber into the equalizing chamber in an amount sufficient to establish the same pressure on both sides of the displaceable wall. Force can therefore no longer be transmitted to the actuating element by way of the displaceable wall. The actuating element is therefore returned immediately to its initial position by the biasing spring. The speed of return does not depend upon the rate of cooling of the expansible fluid, but is largely governed by the speed at which the expansible fluid is able to pass from the working chamber into the equalizing chamber.

It is particularly advantageous if the expansible fluid is constituted in known manner by a liquid vapor charge and if the connecting passage begins at the vapor zone of the working chamber, at least when the thermal actuator executes its maximum stroke. An expansible fluid of this kind not only possesses the usual advantages whereby vapour is generated when it is heated and the vapour pressure is used for the purpose of actuation. In the present context the vapor flows more rapidly than the liquid into the equalizing chamber after the valve has been opened, so that a particularly rapid return movement is achieved.

When the pressure has been balanced on both sides of the displaceable wall and this wall is returned to its initial position by the action of the spring, part of the expansible fluid that has been transferred to the equalizing chamber can be returned to the working chamber even while the return movement is taking place. Other auxiliary means, e.g., a small pump, can be provided for the purpose of returning the expansible fluid from the equalizing chamber to the working chamber after the return movement of the thermal actuator.

When a liquid vapor charge is used, it is preferred to position the equalizing chamber substantially above the liquid zone of the working chamber. The vapor condensing in the equalizing chamber then flows simply by gravity from the equalizing chamber into the working chamber.

A particularly suitable valve is a magnetic valve. This can be easily actuated, especially as only an on-off action is necessary for the rapid return of the actuator.

A particularly simple form of construction is achieved if the connecting passage passes through the displaceable wall, and the valve case is securely connected to this wall. This results in an extremely short connecting passage offering little resistance to flow. Nor is a complicated lever system required for guiding the closing member of a magnetic valve, secured in the working chamber, against the displaceable wall.

In particular, the displaceable wall may be disposed substantially horizontally but may slope slightly inwardly to form a cone, and the connecting passage may begin at the middle of the cone. The displaceable wall can then be used as a collecting surface for the condensate from the expansible fluid that flows downwards into the working chamber.

Furthermore, the valve casing may constitute the mechanical connexion between the displaceable wall and the actuating element. This further simplifies the construction.

The magnetic valve may incorporate a plunger type armature which forms the closing member, no intermediate part being required. In such arrangements, the connecting passage may extend along the plunger type armature and the latter may be of polygonal cross section or contain axial grooves in its surface.

The heating device is expediently fitted in the lower portion of the working chamber. When a liquid vapor charge is used, this device is always positioned in the liquid zone. The heating device may for example be a heating coil fitted concentrically with the actuating elements. This results in symmetrical conditions.

Particularly advantageously, a FTC-heating resistor is used as the heating device. This heating resistor automatically adjusts the heating power supplied, so that no excess pressure can occur in the system.

A further possible way of effecting control consists in providing, in the heating current circuit, a pressure monitor which monitors the pressure in the working chamber or the difference between the pressures in the working and equalizing chambers. By adjusting the pressure monitor from the exterior it is possible to vary the stroke when a return spring having a specific characteristic curve is used. However, even in the case of a specific stroke limited by fixed stops, the pressure monitor ensures that no excess pressure develops.

. A further possible way of preventing excessive heating consists in providing, in the heating current circuit, a limit switch which breaks the heating current circuit when an upper end position is reached.

A further possible way of adjusting the end position of the thermal actuator, consists in using an adjustable spring for acting on the actuating element.

The actuator may execute relatively long strokes. For this purpose the displaceable wall is expediently sealed off by means of a rolling diaphragm or a bellows.

The invention will now be described in greater detail by reference to two embodiments illustrated in the drawing, in which:

FIG. 1 is a longitudinal section through a first embodiment, and

FIG. 2 is a longitudinal section through a second embodiment.

The thermal actuator seen in FIG. 1 has a casing consisting of a body 1 and a cover plate 2. By means of a displaceable wall 3, which is sealed off from the wall of the casing with the aid of a bellows 4, the interior of the casing is divided into two chambers, namely a working chamber A and an equalizing chamber B. The thermal actuator comprises an actuating element in the form of a valve stem 5, at the lower end of which is fitted a closing member 6 since it coopertes with a valve seat 7. The valve stem is mounted in a guide 8 at the lower end of the body 1 of the casing. This output point is sealed with the aid of a bellows seal 9. The displaceable wall is connected to the valve stem 5 by way of the case 10 of a magnetic valve 1 l. A return spring 12, fitted in the equalizing chamber B, biases the displaceable wall 3 and therefore the valve stem 5 in the downward direction.

The working chamber A and the equalizing chamber B are interconnected by a passage 13. This passage comprises a valve seat 14 which can be sealed off by the plunger type armature 15 of the magnetic valve 11. The connecting passage extends along the plunger type armature which, for this purpose, has a polygonal cross section, said passage being extended by transverse holes 16 in the valve case 10.

An electric heating coil 17 is fitted beneath the valvecase. Current is supplied to this heating coil and to the magnetic valve through conductors 18 which run out through a pressure-tight duct 19 in the body 1 of the casing.

Also provided is a pressure monitor 20 which enables the heating current to be cut off when the pressure in the working chamber A or the difference between the pressures in the chambers A and B rise above a predetermined level.

In the non-operating position as illustrated, the Work ing chamber A is partly filled with a vaporizable liquid e.g., a fluorochloro hydrocarbon such as R 11. Thus a liquid zone 21 is formed in the lower portion of this chamber, and above this a vapor zone 22.

This thermal actuator operates in the following manner: in the illustrated position with the magnetic valve 11 opened, the pressures in the working chamber A and the equalizing chamber B are balanced. The closing member 6 is pressed on to the seat 7 by the force of the spring 12. If the magnetic valve 11 is now closed and current is applied to the heating resistor 17, part of the liquid 21 evaporates as a result of its being heated. The pressure in the working chamber A rises, and the displaceable wall is pressed upwards, thereby overcoming the force of the spring 12, and the closing member 6 is also moved. This movement is terminated either by a mechanical stop, e.g., when the closing member 6 moves on to the guide element 8, or the movement ends when equilibrium is established between the heat supplied and the heat dissipated by the casing 1, 2. In the latter case, the closing member 6 remains in a position which is determined by the force of the spring 12 and the force generated by the vapo pressure. When the closing member bears against the stop, the heating power can be monitored in the open position by the pressure monitor 20 which always switches off the heating power when the pressure rises above a prescribed level, the monitor switching on the heating power again when the pressure drops below this level. The magnetic valve 11 is de-energized for the purpose of rapidly closing the valve 6, 7. The connecting passage 13 leading to the equalizing chamber B is thus opened. Since the transverse inlet holes 16 forming part of this passage communicate with the vapor zone 22 asa result of the upward displacement of the wall 3, vapour flows very rapidly through this passage into the equaiizing chamber B. Thus pressure is equalized on both sides of the wall 3. Only the spring 11 continues to apply force and impresses the closing member 6 rapidly on to the valve seat 7. At the same time the heating means is switched off. Cooling then takes place. The vapor that has passed into the equalizing chamber B condenses on the cover plate 2 and flows back through the valve opening 14 and the connecting passage 13 into the liquid zone 21 of the working chamber A. The initial position as illustrated is thus reached again.

In the arrangement shown in FIG. 2, the casing consists of a lower part 23, a median part 24 and an aluminium upper part 25. These parts are interconnected by screws 26 and 27. Between the lower part 23 and the median part 24 is clamped the outer flange of a rolling diaphragm seal 28, and between the median part 24 and the upper part 25 the flange of a rolling diaphragm seal 29. The rolling diaphragm seal 28 is held between two clamping nuts 31 and 32 screwed on to an actuating rod 30.

The inner portion of the diaphragm 29 is clamped between a displaceable wall 33 and the case 34 of a magnetic valve 35. The working chamber A and the equalizing chamber B, formed in the same way as that described in connexion with FIG. 1, are interconnected by a passage which consists of a transverse portion 36 and a longitudinal portion 37. Here again, the plunger type armature 38 of the magnetic valve constitutes the member for closing a valve opening 39. The working chamber A is filled with a vaporizable liquid 40. Heating is carried out with the aid of a FTC resistor 41. The conductors 42 running to the heating resistor 41 and the conductors 43 supplying current to the coil of the magnetic valve 35 pass through openings 44 and 45 respectively in the median part 24 of the casing, these openings being filled with a plastics material applied in the liquid condition. A vapor zone 46 is located above the liquid 40. The return spring 47 is fitted beneath the lower part 23 of the casing. A backing element 48 for the spring can be displaced along the rod 30 with the aid of a nut 49, so that the bias of the spring can be adjusted.

The mode of operation of this thermal actuator is the same as that of the actuator illustrated in FIG. 1. A description is therefore unnecessary. Very long strokes can be obtained with the aid of the rolling diaphragms. The FTC heating resistor automatically regulates the heating power. Any required operating element can be connected to the actuating rod. This element need not necessarily be a closing member for a valve, but may be the axial piston of a pump, for example. The mag tic valve is preferably made of moulded plastics material, e.g., a polyamide. The lower part 23 and the median part 24 of the casing can be made of the same material. The upper part 25 of the casing is preferably made of metal so as to accelerate condensation.

The displaceable wall 33 is of conical shape so that the downwardly flowing condensate can be collected and returned to the liquid 40 in the working chamber A through the passage 37, 36.

I claim:

1. A thermal actuator comprising a casing, adjacent expansible equalizing and working chambers separated by a movable wall, said chambers being in fluid tight relation relative to said casing, spring means biasing said wall in one direction, an actuating member connected to said wall, fluid passage means between said chambers, selectively controllable valve means for said passage means for selectively providing fluid communication between said chambers, an expansible fluid in said working chamber which expands to move said wall in the opposite direction when said valve means are closed, and heating means for heating said fluid.

2. A thermal actuator according to claim 1 including electromagnetic means for operating said valve means.

3. A thermal actuator according to claim 1 wherein said fluid passage means is in said wall.

4. A thermal actuator according to claim 3 including a housing for said valve means, said housing being fixedly connected to said wall.

5. A thermal actuator according to claim 4 wherein said housing is a rigid link between said wall and said actuating member.

6. A thermal actuator according to claim 1 wherein said casing forms a well for said working chamber for holding the liquid portion of said expansible fluid, said heating means being in said well beneath the surface level of said liquid portion.

7. A thermal actuator according to claim 1 wherein said heating means is a PTC resistor.

8. A thermal actuator according to claim 1 including pressure monitoring means in said equalizing chamber, said heating means being controlled by said pressure 

1. A thermal actuator comprising a casing, adjacent expansible equalizing and working chambers separated by a movable wall, said chambers being in fluid tight relation relative to said casing, spring means biasing said wall in one direction, an actuating member connected to said wall, fluid passage means between said chambers, selectively controllable valve means for said passage means for selectively providing fluid communication between said chambers, an expansible fluid in said working chamber which expands to move said wall in the opposite direction when said valve means are closed, and heating means for heating said fluid.
 2. A thermal actuator according to claim 1 including electromagnetic means for operating said valve means.
 3. A thermal actuator according to claim 1 wherein said fluid passage means is in said wall.
 4. A thermal actuator according to claim 3 including a housing for said valve means, said housing being fixedly connected to said wall.
 5. A thermal actuator according to claim 4 wherein said housing is a rigid link between said wall and said actuating member.
 6. A thermal actuator according to claim 1 wherein said casing forms a well for said working chamber for holding the liquid portion of said expansible fluid, said heating means being in said well beneath the surface level of said liquid portion.
 7. A thermal actuator according to claim 1 wherein said heating means is a PTC resistor.
 8. A thermal actuator according to claim 1 including pressure monitoring means in said equalizing chamber, said heating means being controlled by said pressure monitoring means. 